The standardization of a small base station that can be installed in user's home, office and the like is currently under way. The small base station is installed in home, small office and the like by a user, and connected to a mobile communication network via a communication line such as ADSL (Asymmetric Digital Subscriber Line) or FHHT (Fiber To The Home). Such a small base station is generally called a femto base station, a femtocell base station, or a home base station. Further, the coverage area of a cell formed by the small base station is significantly smaller than that of a macro cell used hitherto. Therefore, a cell formed by the small base station is called a femtocell, a home cell or the like.
The 3GPP (3rd Generation Partnership Project) Release 8 standardizes such a small base station as Home Node B (HNB) (see Non Patent Literature 1). A cell formed by HNB (which is referred to hereinafter as HNB cell) is called CSG (Closed Subscriber Group) cell in some cases. Only a pre-registered user equipment (for example, a user equipment used by an owner of HNB or its family) can be basically connected to the CSG cell, and another user equipment cannot be connected thereto.
Thus, a macro user equipment (MUE) that belongs to a macro cell receives downlink interference in the vicinity of the HNB cell (CSG cell) to which it cannot be connected. A problem thus occurs that the interference causes degradation of the downlink communication quality in the MUE.
A technique to address the above problem is disclosed in Non Patent Literature 2. Specifically, the MUE transmits “Measurement Report”, which is one of RRC (Radio Resource Control) messages, to RNC (Radio Network Controller) upon receiving downlink interference. The RNC instructs the HNB cell that serves as the source of interference to adjust a transmission power.
It is noted that, in the following explanation, the small base station as described above is generically referred to as “home base station”, and a cell formed by the home base station is referred to as “home cell” in some cases. Further, a base station that forms a macro cell is referred to as “macro base station” in some cases for differentiation from “home base station”. Furthermore, a user equipment that can be connected to “home cell” is referred to as “home user equipment” in some cases for differentiation from “macro user equipment”.